1. Field of the Invention
This invention relates generally to a system and method for determining the presence of elements and their distribution in a specimen, and pertains more particularly to the use of a particle beam for producing X-rays characteristic of the elements and a color code for visually identifying the elements in accordance with the position of the electron beam.
2. Description of the Prior Art
X-ray elemental maps using a monochrome cathode ray tube display have been used rather widely for the last eight years or so, and are commercially available from several manufacturers. Such systems currently on the market rely on the processing of an X-ray signal, either with an energy selective detector or a crystal spectrometer, which has been generated by the action of a finely focused electron beam. In such equipment, signals are derived from the X-rays within an energy range corresponding to the excitation of a single elemental species and spots of light are produced at a location on the display which corresponds to the position of the electronic beam. However, all X-ray signals generated by the sample or specimen that correspond to different elements contained in the specimen are lost other than the one selected for investigation. Also, there is no distinction made between fluorescent X-rays, which are characteristic of each element and which are therefore of critical interest, and bremsstrahlung X-rays which represent an unwanted background as far as mapping is concerned and when present to any degree make the fluorescent X-rays, which identify the element or elements, virtually indistinguishable from this background.
Accordingly, nonmapping techniques have been resorted to for simultaneously recording X-rays characteristic of a range of elements. Such techniques make good use of the X-ray information, but the spatial information provided by the electron microscope is degraded because only recording spot measurements or area measurements within the field of display are utilized.
Because of the shortcomings of the techniques alluded to above, sometimes a fully electronic method of simultaneously recording the spatial position of the electron beam and the energy of each X-ray is employed. The disadvantages of this technique resides in the need for accumulating an extremely large amount of data which must be processed and the concomitant problems of recreating a map presentation from such large amounts of digital data. Owing to the fact that techniques of this type involve an inordinate amount of time and cannot provide an elemental concentration map quickly enough to enable decisions to be made as to further measurements from the sample while it is still in the microscope, considerable reluctance is usually experienced with respect to using a system, especially because of the cost of the equipment and the nonuse of such equipment for other projects while the large quantities of data are being processed.